This invention pertains generally to antennas for radio frequency energy and particularly to directional antennas wherein the active elements are interconnected electrically to form a grid of radiating and conductive members.
It has been proposed, as outlined in an article in the IEEE "Transactions on Antennas and Propagation," January 1964, by Kraus, that the conductor of a microstrip transmission line be disposed in a grid-like pattern to form an array antenna for radio frequency energy. In the just-mentioned article, the contemplated grid-like pattern appears to form a planar array of similar rectangular meshes with each mesh having longer sides equal in length to one wavelength and shorter sides equal in length to one-half wavelength. Further, the longer sides of adjacent meshes are contiguous to form columns of rectangular meshes with the shorter sides of the individual rectangular meshes in alternate ones of the columns being staggered to be connected at the center of the longer sides of the contiguous rectangular meshes in the adjacent columns. Various specific arrangements where grid-like structures are positioned over a metallic ground plane with air as the dielectric are shown by Kraus in U.S. Pat. No. 3,290,688.
Although printed circuit array antennas built following the principles set out by Kraus and others have proven advantageous, particularly in many of those applications in which physical size, ease of fabrication and ability to operate at elevated temperatures are controlling characteristics, there are some applications in which deficiencies of such antennas have heretofore militated against their use. Specifically, an array antenna being discussed often may not be used in a guided missile wherein space is at a premium and ambient conditions are adverse.
The key deficiencies suffered by known array antennas of the type being discussed are: (a) an extremely narrow bandwidth; (b) a susceptibility to cross-polarization; and (c) an inability to control amplitude taper, thus resulting in excessively high sidelobes. These deficiencies, either alone or in combination, so overbalance the desirable characteristics of any known printed circuit antenna that only conventional slotted or stripline arrays are presently used in guided missiles, especially when monopulse characteristics are desired.